In the field of potable water systems, there is a continuing need for improvement in an electrically driven water pump that can be used for systems of the demand type; that is, a system in which there is a remote store of potable water which may be gravity fed or stored in any source which does not require the water supply to furnish water at a required outlet pressure at a desired flow rate. Such systems are often referred to as demand systems.
The need for improvement is particularly apparent in the case of demand systems for use on aircraft where the supply of water is desired to be maintained at or near ambient pressure in the aircraft rather than under pressure. This substantially reduces the possibility of leaks from a fully pressurized tank of water or from any of its distribution conduits, which deliver pressurized water to any distribution point. Aircraft and their systems are subject to the repeated cycling of ambient pressure which occurs during the normal takeoff, flying at cruising altitude and in landing. Repeated cycling of pressurized structures gives rise to joint failure, particularly where the conduits and joints are at an elevated delivery pressure rather than static ambient pressure.
Demand systems are especially useful for supplying cold and hot potable water where the heater is similarly of the demand type and where there is not a large volume of potable water maintained at delivery pressure and use temperature. The combination of the demand pump and the demand heater with a non-pressurized potable water source present the ideal combination for supplying hot and cold potable water aboard aircraft.
Faced with the foregoing state of the art, we have produced an integrated pump/motor in which potable water flow provides lubrication and cooling of the pump and motor by employing the potable water itself without danger of contamination of the water delivered.
We have also sought to produce a compact pump motor combination weighing just a few pounds and having a system capable of delivering on demand a flow of potable water at flow rates as high as 4 to 6 gpm.
We further sought to design an integrated pump motor in a way in which any ferrous metallic laminations are cooled by the flow of potable water without the danger of corrosive rusting of the laminations.
A further objective is effective cooling of the motor windings while maintaining the windings fully insulated from the cooling flow of potable water.
It is a further object of the invention to provide cooling of all bearings and other rotating surfaces in the motor and in the pump by potable water.
A further objective of the invention is to provide a path for cooling water to flow through the pump/motor shaft after lubricating and cooling all bearings, windings, laminations, and the motor shaft, thereby circulating potable water back into the incoming water stream.
A further objective of the invention is to provide for expansion of water when water inside of the pump freezes, thereby preventing damage to the pump from freezing water.
A further objective of the invention is to provide a means to remove electrical power from the pump when the pump is energized while frozen, thus preventing damage due to overheating of the pump.
Each of these objects and design objectives are accomplished in the combination of a centrifugal pump with an electrical motor assembly mounted on a main hollow shaft in a sealed housing in which an annular potable water output manifold includes a port for a lubricating water passage between the rotating and static components of the motor within its housing. The annular output manifold communicates with a second manifold area and continuing flow paths between the pump/motor shaft and a cylindrical bearing at the end of the motor assembly adjacent to the pump. The flow paths continue between the cylindrical bearing and an anti-thrust bearing and further extend through a gap between seals protecting the motor stator windings and laminations and the rotor laminations.
The potable water paths for lubrication continue through a second chamber in the motor assembly and between the rear cylindrical bearing and the rotor shaft, returning through the hollow rotor shaft and through a hollow fastener which secures the pump to the motor drive shaft and back into the potable water output manifold. This series of potable water lubricating paths provide lubrication between all rotating parts of the pump and motor and adjacent non-rotating parts, and provides a recycle path for the lubricating portion of potable water flow, which returns to the main potable water delivery path.
An expansion chamber within the sealed housing allows for expansion of water within the pump if the pump is operated under freezing conditions and the water begins freezing.
A thermal switch located in the motor of the pump causes electrical power to be removed from the pump when the motor of the pump becomes over heated, for example by a locked rotor due to ice formation in the water cooling passage.